Because there was no activity - wind or other - on Devils Lake, the water surface was flat. This condition caused the water to act as a mirror. This phenomenon is known as glassy water. When glassy water conditions exist, humans are not able to judge, with accuracy, the distance to the surface of the water by looking at it. In this occurrence, the pilot was trying to land on a surface an unknown distance below the aircraft. The helicopter was still travelling forward and down at a rate that caused the floats to dig into the water on contact, and the helicopter flipped over, likely around the left front corner. When the main-rotor blades struck the water at normal rpm (a tip speed of about 750km/h), one blade broke and skipped on the surface of the water. As the helicopter continued to pitch forward and roll left, it rolled onto the broken blade. The blade penetrated the front of the helicopter, and wreckage debris struck the pilot and the front-seat passenger on their heads. The pilot was wearing a helmet, which protected him from serious head injuries. The front-seat passenger received critical head injuries. Recent underwater emergency escape training gave the conscious passenger the knowledge and experience he needed to help him remain calm, escape safely, and rescue the unconscious passenger from the submerged wreckage.Analysis Because there was no activity - wind or other - on Devils Lake, the water surface was flat. This condition caused the water to act as a mirror. This phenomenon is known as glassy water. When glassy water conditions exist, humans are not able to judge, with accuracy, the distance to the surface of the water by looking at it. In this occurrence, the pilot was trying to land on a surface an unknown distance below the aircraft. The helicopter was still travelling forward and down at a rate that caused the floats to dig into the water on contact, and the helicopter flipped over, likely around the left front corner. When the main-rotor blades struck the water at normal rpm (a tip speed of about 750km/h), one blade broke and skipped on the surface of the water. As the helicopter continued to pitch forward and roll left, it rolled onto the broken blade. The blade penetrated the front of the helicopter, and wreckage debris struck the pilot and the front-seat passenger on their heads. The pilot was wearing a helmet, which protected him from serious head injuries. The front-seat passenger received critical head injuries. Recent underwater emergency escape training gave the conscious passenger the knowledge and experience he needed to help him remain calm, escape safely, and rescue the unconscious passenger from the submerged wreckage. Glassy water conditions impaired the pilot's ability to judge his height above the lake, and during the landing, the helicopter's floats contacted the water before the pilot expected them to, dug in, and the helicopter flipped over. One of the helicopter's main-rotor blades broke on contact with the water and penetrated the front of the helicopter. Wreckage debris struck the pilot and the front-seat passenger on their heads.Findings as to Causes and Contributing Factors Glassy water conditions impaired the pilot's ability to judge his height above the lake, and during the landing, the helicopter's floats contacted the water before the pilot expected them to, dug in, and the helicopter flipped over. One of the helicopter's main-rotor blades broke on contact with the water and penetrated the front of the helicopter. Wreckage debris struck the pilot and the front-seat passenger on their heads. The pilot was wearing a helmet, which protected him from serious head injuries. Recent underwater emergency escape training contributed to one passenger's ability to safely escape from the helicopter and rescue the other passenger from the submerged wreckage. A satellite telephone was available; this contributed to prompt accident scene response.Other Findings The pilot was wearing a helmet, which protected him from serious head injuries. Recent underwater emergency escape training contributed to one passenger's ability to safely escape from the helicopter and rescue the other passenger from the submerged wreckage. A satellite telephone was available; this contributed to prompt accident scene response.